Rapid Screening Procedure for Methionine Levels in Maize and Soybean

Abstract

Methionine is an essential amino acid critical to human, livestock, and poultry nutrition. A microbiological method has been tested for use as a rapid, inexpensive, and reliable means of screening maize (Zea mays L.) and soybean [Glycine max (L.) Merr.] seed for methionine concentration. Maize and soybean meal samples with various methionine contents were defatted before enzymatic proteolysis. An aliquot of each hydrolyzate was added to liquid media free of methionine, autoclaved, and inoculated with a bacteria auxotrophic for methionine. After incubation for 20 h, the turbidity of the cultures was measured and methionine concentration was calculated from standard curve data. Significant positive correlation (r = 0.74 maize; r = 0.88 soybean) was found between the microbiological and chemical determinations. These results demonstrate that the less expensive microbiological procedure would have great utility in a methionine enhancement plant breeding program.

Recurrent Selection to Alter Grain Methionine Concentration and Improve Nutritional Value of Maize

“…Microbial methods have been shown to be effective for screening for amino acid levels in grain (Wright and Orman, 1995). We used a microbial analysis method to analyze each sample as follows.…”

“…One reason recurrent selection for methionine has traditionally not been used extensively is the amount of labor and expense involved in measuring methionine concentration by HPLC. However, microbial methods are inexpensive, adaptable to high‐throughput analysis and have been shown to be effective for grain analysis (Wright and Orman, 1995). High throughput microbial methods have been used for the analysis of commercial maize hybrids (Darrigues et al, 2005) and germplasm from a QPM breeding program (Scott et al, 2004).…”

Interaction of Genetic Mechanisms Regulating Methionine Concentration in Maize Grain

“…Following incubation for 8 h at 37°C, the growth of each culture was determined by measuring its turbidity at 595 nm using a spectrophotometer. Culture turbidity measurements have been shown to be a reliable estimate for methionine concentration compared with standard AOAC determinations with turbidity measurements being proportional to amino acid concentrations (Wright and Orman, 1995). Each of the grain samples produced in 2010 and 2011 at Ames, IA, were analyzed for methionine concentration along with protein, starch, and oil concentrations predicted by NIRS using a Foss Infratec 1241 grain analyzer (Foss NIR Systems, Inc.).…”

Breeding for Grain Amino Acid Composition in Maize

“…They used the bacteria Pediococcus cerevisiae, which is auxotrophic for methionine, and measured the turbidity, a representation of bacterial growth, as an indication of the methionine content in the sample. Although this method may not provide the best analytical accuracy, it provides the high throughput required by plant breeders (Wright and Orman, 1995). Hernandez and Bates (1969) determined that microbial assays and chromatographic techniques used in the determination of tryptophan were expensive, tedious, and time consuming.…”

“…The microbiological method for the determination of methionine in maize kernels is similar to that described by Wright and Orman (1995). An auxotrophic strain of Escherichia coli, P4x, was used in this assay.…”